Elevation meter



Aug. 4, 1953 F. rJOHNSON ErAL ELEVATION METER Filed Sept. 26, 1947 l0Sheets-Sheet l 3H w Sh R s Y E R MMV m mOA. m JM LM. h 3m Sm D .KN Fmw 8N2 QN m NK N m f ELEVATION METER Filed Sept. 26, 194'? 10 Sheets-Sheet 2'INlV/ENTORS FORD L. JOHNSON a FRED M. MA yes C-Y ATTOR EYS fwn Aug. 4,1953 F. L. JOHNSON ETAL ELEVATION METER 10 Sheets-Sheet 5 Filed Sept.26, 1947 INVENTORS FORD JOHNSON a FRED MAyEs BY Y w ATTR YS Aug. 4, 1953F. l.. JOHNSON ETAL 2,647,323

ELEVATION METER Filed sept. 2e, 1947 I 1o sheets-sheet 4` l' IIIIIIIIIIII l f zLs-/p I 262 INVENTORS FORO L. JOHNSON 8 650 M MAYES Aug. 4, 1953F. l.. J`oHNsoN Erm.

ELEVATION METER 10 Sheets-Sheet 5 Filed Sepl'.. 26; 1947 INF/mmm vFORDL. JOHNSON 8' FRED M MAyE-S .lill NNN www Aug. 4, 1953 F. l.. JoHNsoNErm. l 2,647,323 i ELEVATIoN METER Filed Sept. 26, 1947 l0 Sheets-Sheet6 KH H L 1 HF H2 fI/ 3 I )l1 2 E L K L I a J.IIIIIIIHIIIIHIIIIHIIIHIllll|III'IIIIIIIIIIIIIIIIIIIIHII||||||||||H|IIIIIIIIIIIIIIIIIIHIIIK. mmmmmmv mum `v v mumu v 1mm L HJIINHl/lmgoiks FORD L. -oH/vso/v r s@$50 M. MA/ES TORN YS l1g 4, 1953 F. L. JOHNSON E-rAL 2,647,323

` ELEVATION METER Filed sept. 2e, 1947 1o sheets-sheet 7 `1NVENT0R5 FORDL. JOHNSON F8650 M. MA ,VES

dal: Y ATTORN YS F. L. JOHNSON -EI'AL Aug. 4, 1953 ELEVATION METER 10sheets-sheet s Filed Sept. 26, 1947 Aug. 4, 1953 F. l.. JOHNSON ErAL2,647,323 I v ELEVATION METER Filed sept. 26, 41947 v 1.oA sheets-sheet9 `1NVENT0RS FORD L. JOHNSON 8 650' M. MAVES ATTORNEYS Aug. 4, 1953 F.L. JOHNSON EI'AL ELEVATION METER 1d sheets-sheet 1o Filed Sept. 26, 1947www yINVENTORJ FORD .J'OH/VSON 8 MAYES g'YI'TORNE'QS Reference willfirst be made to the preferred type of apparatus illustrated in Figures1 to 10, inclusive. Before proceeding with a discussion of the theory ofoperation the apparatus itself will be described in detail andthereafter there will be indicated the mode of attainment of measurementof elevation differences.

Reference will first be made to Figures 1 to 6, inclusive, involving themaintenance of a pendulum constantly perpendicular to a path of movementof the apparatus despite inclinations of that path, the maintenance ofperpendicularity being in a statistical sense: i. e., the pendulum is onthe average perpendicular to the path. In Figure 1 the pendulum assemblyis diagrammed to show connections to electrical circuits. As illustratedin detail in Figures 2 to 6 the pendulum consists of a rectangular coil2 of a large number of turns of wire supported by light spring brassstrips 4 and 6 of Z or other cross-section to giye rigidity, except attheir upper ends where they are extended in the form of thin (0.061inch) very flexible strips to provide fulcra of very little stiffness.These strips 4 and have their fiexible upper ends clamped in aninsulated portion of a supporting structure 8 which is adapted to berigidly mounted on the frame of a trailer to which reference will bemade hereafter. When the trailer is on horizontal ground the pendulumwill be vertical. When the trailer is on sloping ground the pendulumwould, if the electrical system were not operating, also take a verticalposition except to the extent to which it would be deviated therefromdue to the slight stiffness of the upper ends of the supporting strips Aand 5. Under the operation of the electrical system, however, a magnetictorque is applied to the pendulum to cause it to assume to a high degreeof accuracy a nonvertical position in which it will be perpendicular tothe plane of the sloping roadway.

Rigidly fixed in the pendulum housing 8 is an iron bar l2 extendingthrough the coil and associated with strong permanent (Alnico) magnetsi4 and I6, each of E shape, to provide, between it and the central polesI8 and 20 of the magnets, an air gap, the flux across which issubstantially uniform. The vertical sides of the coil 2 move in this airgap. As illustrated, the end poles of the magnets, all of which are ofthe same polarity and opposite the common polarity of the central poles,are in contact with the member l2.

Associated with the magnetic system just described is a second magneticsystem comprising an E-shaped laminated core portion 22, the end polesof which are bridged by a laminated core section 28 which is embedded ina slot in the bar i2 and spaced from the central pole 2S of the coresection 22 to provide an air gap in which moves the lower side of therectangular pendulum coil 2. A winding 24 surrounds the pole 26 toprovide an alternating flux through the laminated magnetic circuit.

The assembly just described is preferably enclosed in a container (notillustrated) filled with a damping oil for the pendulum. Adjustablestops 25 limit the pendulum movement to prevent damage thereto. Theadjustment in practice may limit the pendulum swing to less than onedegree.

An oscillator 30 comprises a pair of triodes indicated at 32 havingtheir elements interconnected in conventional fashion by resistors 33and condensers 34 to provide a multivibrator which is connected tc atuned tank consisting of inductance 36 and condenser 3'1. As will beevident hereafter the frequency of this oscillator is not criticalinasmuch as its output, used for phase detection, is not ultimately usedfor its frequency value but gives rise to a direct control potential.Consistent with convenient and practical construction of the pendulumassembly the frequency of this oscillator may be of the order of iive tofifteen kilocycles per second. It will. of course, be evident that theoscillator may be replaced by any of a large number of types ofoscillators well known to the art.

The output from the oscillator 3i! is delivered through the transformer38 to the driver coil 24 of the pendulum assembly heretofore described.The current in the driver coil will induce in the circuit of detectorcoil 2 currents which will vary with the position of the detector coil.When the pendulum is in its normal midposition corresponding toperpendicularity to the roadway, the signals induced in the detectorcoil will be at a minimum but, as in the case of most alternatingcurrent bridge or balance arrangements, the signals will not be reducedto zero but rather will contain harmonics of the fundamental frequencyand a minor component of the fundamental frequency out of phase with thenormal signal which would be produced with deviation of the pendulumfrom the perpendicularity mentioned.

The output from the detector coil is fed through the lines 68 and l2 andcondensers 43 to the primary of a transformer All, the secondary ofwhich delivers the signals to an amplifier through a band pass filterindicated at Dit. The elements of this band pass filter, for example itscondensers, may be adjusted to secure the desired phase characteristicsof the signals at the oscillator frequency which is used. As will beshortly evident, adjustment of the phase relationships will be helpfulin securing the best responses of the detector system. The signals fromthe filter 46 may have their amplitudes varied by adjustment of thecontact Si) of the potentiometer 48 for feed thereof to the first stagetube 52 of an amplifier' which comprises an additional stage 55,coupling being provided through a circuit 54 tuned to the signalfrequency. The remaining characteristics of this amplifier are quiteconventional. ts output feeds the primary of a transformer 56 which hasa pair of secondarles 53 and 60, corresponding ends of which areconnected to the respective anodes 52 and B4 of the triode elementswhich may be included in a single envelope 6B. The transformerconnections are such that the anodes are at any instant of the samepolarity. In order to render the circuit phase-sensitive, the grids 58and 10 of the triode elements of the tube 66 are respectively connectedthrough the lines l2 and 'I4 to the terminals of a secondary 'I6 of atransformer '51, the primary T8 of which is fed by an amplifiercomprising the tube 8U, the grid of which is connected through apotentiometer 8l and the line 82 with the secondary of the transformer38. An adjustable resistor 83 connects line 82 with a center tap on thesecondary of the transformer lill to balance out-ofphase signals.Disregarding for the moment the residual signals which appear in thedetector coil 2 when this coil is in its normal null position, thedeviation of the pendulum coil from such position will result in theproduction of an induced signal voltage therein having one phaserelative to the oscillator if deviation occurs in one direction andopposite phase if deviation occurs in the other direction'.- f it is`assumed that. in af--particular halfcycle the anodes-E-andlla-arepositive and inthis same half cycle-the grids S82 and 'iii :are"respectively" positive'and negative,

then during that half cycle the-triodelhaving the anode S22' will l beconductive'rvvhile the. triode having the anode 64 will' benoneconductive'. During the next half cycle, despite` reversal of thegrid potentials, both anodes will be negative so'that neither triodewill conduct.

O'n-the other' hand, ifl'we assumea 'half cycle corresponding to the rstonejust"mentioned` in which v. grid (5811 is positive andi grid "i8:negati-ve', ,if the pendulum has vdeflectedin the opposite direc@- ticnboth anodes will vbe negative and no current Will iioW in eithertriode,In the nextfhalfcycle both anodes will be positive and grid 10'"Will'ibe positive and gridV STE' negativeso thatthe "triode whichYincludes the anode 1615i will' be conductive While the triode whichincludes the anode 62-fwill remain Inon-conducti=ve- Thus in a completecycle one or'the" other of' the triodes is conductive depending upon thedirection ofdeviation ofthe pendulum fromnormalposition. The result ispulsatingy ourrentlow through one or the other of'the resista-noosto`and`88 andthe common-cathode resistor 842 The operation is essentiallysimilarevenfthough residual'signalsare' deliveredfrom the detectorlcoil.If the amplicatin system is operated' as a limiter, the disturbingei'ect of these Aresidual signals is not detrimental and, in fact,due-to the limiting action inminimizing the'effe'cts :of amplitudetransients' the overall performance Yi's even more satisfactory; Anextreme-sensitivity and @2 to give-rise to negative -potentials'withrespect to ground in the lines 96 andt'depending upon respectivecondnctivity through anodes B2"and 6d. A pair ordiodes ed lfia-ve'theirlanodes connected to the lines $36 and 98 so as to ground these linesinthe event they becoine'po'sitive with respect to ground.

The lines et and $3 are connectedto the control grids itil' andIZ'ofgas-lled tubes INIv and IUIS,V for example of 2050 type. The'connections of these tubes may be 'novvl briefly described. The directhigh voltage supply is connectedto the anodes of the respective tubesthrough resistances iii? and II li, there being located between thevancdes and ground the respective'condensers lvand '.125'. The propernormal-biases areapplied to the `control grids ofthe tubes `by'ra'isirigthe potentials of their cathodes abovelground by connection to the pairsof resistances, I I Wand I 'I '1, and H8 and IIE?.` Resistances Ii-iivand IISare adjustable. Examination ofthe gas tubecii-'cuit's willrevealthat they are so'connected"that if nothing elsewere involved, theyWouldpuls'eV due to high resistances` at H2v and' IIA-'in conjuncu tionwith the condensers I 2'3` andv IZ. If the signal ampliiier input wasshort-circuited, adL justrnents at IIS and II8 could'be'made so'ithatthey ywould pulse simultaneously at'approximate'- ly'the same rate.Actually the theoretical pulsingV frequencies are ofvnoconsequence sincethese tubesdo not actuallypulseas theymiglitindependently of signalinput, though theiroperation is dependent upon the ability toso pulse.As'- sume a direction of pendulumdisplacementLV such thatduetotheAphase-detecting arrangement-:al-

ready described theftubeV I 0'4" hasf'appl-ieo. toxitsgridL'azlargeinegativefbiasfso that: it: lcannot nre. Thegridmfi' tube:I IIB however, pisv connected to the linef98 which is'inovv-Vsubstantiallyat groundpotential-and its'grid thas onlyra small negativebias with rrespect Ito .its :cathode so? thatv thisr tube :can pulse'.A'svwillbe shortly evident the only pulse or anyrvconsequence in'. thepulsing period is the n'rst one; fromt they standpointzzofi desirediresults.

Obviously," if the-t pendulum deviates from its nullflplositionsiniftheopposite-.direction the tube AIili will be` -biasedto ran extentpreventing pulsing while the tubefI M'may. pulse;

Theilcutputs .from thegas tube'.- circuits. are de.- liveredlifromitheiranodeszthrough the :condensers |241A and? 'I-26. From'. these`condensers. extend the `respective"lines. I 20.E andy I 22Whichzarejconneoted to a flip-flop arrangement comprising a pair: oftriodes'l I32. and I34f having ther anodes connected'- to a positivevoltagey supply through: a balancing: potentiometer and. having theirgrids I Zil'anidv ISI respectively-.connected to. the lines liIl'andA|22;` Resistance-capacity networks IM. and |313? provide conventionalcriss-cross connections .between the' grids and theV anodes it and Mii.Cathoderesistors ylllliand I4@ are provided. These and other connectionsof this Iflip-flop :ar-"- rangement are conventional, the grids beingycon-- nectedithroughresistors |39. and vIVII'Ito ahigh negative biasingpotential. The' nip-flop characteristicstarey conventionalin that it hasonly two 'stable' states, with one or the other of the triode elements?conducting. If a negative :pulse is appliedto the gridof thetriode'whichisconducting at any instant la' shift occursrresulting inthecutting'o'i ofthe previously conductingv triode and.l in theconductivity of the previouslyfnonconductingtriode: Theleie'ctof theconnections t'o the gas tube'pulsingfsystem will now be clear. Firing ofthe tubefl IM,` -for example; williproduce a negative pulse-ion thegridI291through the icondenser 12m It thetube I32` was conductingthisnegative pulse Will drivev` it.` to cut-oi? condition and 'thetube |34Will become conductive.y It will be evidntthat only the nrst' oi"y aseries of'pulses through theftiibe |04'- Will'haveanyeiiect: once thersti pulse produces vcut-off' of the' tube |32 succeeding' pulses Will-7eifectno change in the flip-fiop circuit. A change inits sta-'ble statevWill occurfonly-f-When a pulse is .emitted frornthe tube Imi,appl-iedvtothe'grid I 3l. Itwill be evident, therefore,- that the tubesI32 and ICM become respectivelyv` conductive as the pendulum swingsthroughv its null position. Actually a slight time delay isinvolvedfwhich willbe described inconne'ction'with a summaryI oftheoperation.

Therestoring of'theidisplaced pendulum is effcted through the circuitcomprising thetriodes i552 and |5222 The grids' 'Hi8' and I5@ of thesetricdes` are respectively. connected through the lines Iiandy I3ilto thegrids IZS'andr I3I in the 'flip-bpicircuit. Obviously, therefore, thegrids offthetriodes |5122 and |54 have thessame poten-'tialsiasthe-grids: IZBland Il: so that las thefastmentionedgridsf-aremaintained, through partic- 'ular"periods,l atcut-off potentials -the saine is true o'ffthe grids |48 and IE6.-Positive anode voltage is supplied to-the triodes |521 and ld". throughthe -vbalancingpotentiomet'er I 5l i from a. voltage regulating circuitcomprising-the triode 53 and the pentode |55,l The respective cathodesof triodes |512 and `I54?areconnectedlinseries with resistors' 'ISS'yandV l''yvhich are, in turn, connected* to ground throughthe'=resistanceY i615. 'Fi'ercontrolgrid of pentode 155 i`s=connected tothe ungrounded end 'of resistor |65;` VAs will be evident hereafter, thecurrent through vresistor IE should be constant since'one or the otherof triodes |52 and |54 should always be conducting the same currentwhile the other is cut off. Despite unavoidable changes incharacteristics of these triodes, and despite variations in the pulsesapplied to the grids, the voltage regulating arrangement insures that,when conducting, both triodes have the same anode currents. To provide arough check on the inclination angle and acceleration a microammeter |6|and series resistance |53V are connectedto provide a voltmeter acrossthe cathodes. Balance of the triodes is attained through adjustment ofthe contact of potentiometer ISI to cause the final differential counterto read zero when the inclination angle is zero.

The anodes of the triodes |52 and |56 are connected through the lines|60 and |62 to the terminals of the detector coil 2 so that a directcurrent will flow in the detector coil in proportion to the differencein potential between the anodes of the two triodes. As will be evident,this current will flow in one direction or the other depending uponwhich of the triodes |52 and |54 is conducting or not conducting, theconnections being so made that this circuit always tends to restore thependulum toward null position'in accordance with the signal to which itsdeviation from null position gives rise. It may be here pointed out thatwhile the high frequency signals are imposed on the lines IBB and |62from the detector coil, one or the other of the triodes |52 and |54 isalways cut oif and the resistance at |5I is suilciently high to preventsuch short circuit-ing across lines |60 and |62 as would prevent thedelivery of proper signals through condensers i3 to the phase detectingsystem. It is, therefore, not necessary to block the high frequencysignals from the lines i60 and |62 by any filtering means.

The description so far covers those elements which control the pendulumoperation and that may be now briefly summarized with references toFigure which indicates typical variations with time 'of conditions inthe apparatus. Assume that the pendulum deviates in one direction fromperpendicularity to the roadway, i. e., from its null position, the termnull being used in this sense herein. The pendulum deviations areindicated by the curve A in Figure l0, the axis representing the nullposition. This deviation prevents the firing of one of the gas tubes andthe other starts pulsing. The signals produced by the deviations of thependulum produce signals on the grid of tube 52 as indicated in curve B.These in turn produce signals on the grids of the respective gas tubes|94 and |85 as indi-cated in curves C and D. C1 and D1 represent,respectively, zero potential, relative to ground, of the grids whichcannot become positive `due to the limiting action of diodes 94. C2 andD2 indicate firing grid potentials. The transients pictured are brieflyreferred to hereafter. Their dotted portions indicate swings ofpotential very great compared with the full line portions of the curves.The resulting plate potentials of tubes |04 and |85, respectively, areindicated in curves E and F. The first pulse of a tube is of largemagnitude, followed by succeeding pulses of less magnitude. Aspreviously described the first pulse of a series will set the conditionof the nip-flop and, by selective cutting olf of one of the tubes |52and |54, will give rise to a direct -current in the pendulum coiltending to lrestore it to its null position by reaction with the thesetime constants are quite small but it will be il (l evident that theoperation is such that the pendulum will pass its midposition beforebeing reversed. The result is that the pendulum can never come to restbut will be continuously oscillating-about the null midposition. Thefactthat the pendulum cannot come to rest eliminates the possibility ofexistence of a dead zone of operation.

The frequency of the pendulum is determined by various factors includingthe amplifier gain, the value of the current applied to the pendulumcoil and the strength of the direct magnetic field, the biases of thegas tubes, the time constants of the circuits 86, and S8, 92, thedamping forces on the pendulum, primarily those imposed by the liquid inwhich the pendulum is immersed, and additionally the amplitude of swingwhich is determined by the same parameters. The pendulum frequency isnot constant. It can have a large amplitude of oscillation at lowfrequency or a small amplitude of oscillation at high frequency, thefrequency changing as the pendulum assembly is tilted. The oscillatingpendulum dissipates the energy supplied by the alternating square wavecurrent which is fed to its coil.

The effects of transients produced by current reversals have not beenheretofore mentioned, but while these transients have large componentsof signal frequency they are prevented from interfering in any way withoperation of the circuit, since they appear as large negative pulses onthe grids of the gas tubes but they occur after the gas tubes havedecided in which direction to move the coil. However, though the effectof these transients is to prevent any further decision by the gas tubesfor a short period of time, the motion of the pendulum is not altered bytheir presence because the-decision of the tubes has already been madeas just described. The method of operation adopted permits an extremelyhigh gain amplifier to be used without the instability which usuallyresults as amplifier gainfis increased. The technique involved is ofquite general application where transient disturbances are fed around afeedback loop. Tests have revealed that the system is entirely free fromthe usual instabilities encountered in amplifiers of this type.

For the purpose of indicating performance of the system certain typicalconditions of operation may be cited. With a natural period ofoscillation of t'he'undamped pendulum of about three cycles per second,satisfactory operation has been found to exist with forced pendulumoscillation frequency in the neighborhood of thirty to seventy cyclesper second with damping provided by a liquid in excess of the criticalvalue for gravitational forces alone. Under such conditions the maximumnormal displacements from the midposition of the pendulum are of theorder of 0.1". As indicated previously, the pendulum may besatisfactorily limited by stops 25 to prevent deviations of more than 1.Adjustments can be readily made to secure oscillation frequencies up tothe neighborhood of three hundred cyclesiper second Withcorrespondingreductionsfin amplitude. Ho\v,everthesehigher frequencies mustheaccompanied by sufficient oscillator Afrecpiency since atthehigherfrequencies ofthe oscillation of the pendulumindividual cycles ofexcitation become Aimportant in determining the reversal points of thependulum, and thisttnds'to leadto instability asthe angle of,inclination ofthe-pendulum unit becomes large. It vqillbe evidentthatall of the time constants in the system aie. quite small. In a typicalarrangement v lhichhas been successfully used the pendulum signal;amountsgto aboutone volt per degree and the, ove1j.all of the signalamplifier is approximately 4,000.

For the kpurpose of securing records. signals are taken from thecathodes of tubes |92 and |34 through the lines .|19 and H2 which areconnected to the respective grids |18 and, ttt of the triodes |82andl84. CurvesI-I and lin-Figure indicate the grid potentials at |89 and|18, respectively, with respect to the cathodelpotentials. The lines H1and I1 represent zero bias, vll-ls and I2 cut-oil for thetriodes, .H3andIs the maximumhias values when the respective flipfop triodes. arenonfconducting, and H4 and 14 the reduced bias values when the latterare conducting. .The last bias values, it isto be noted, are beyondcut-off. ,A positive potential v is applied to the anodes, of triodes`|82 and |S4throughthe load resistors |85 and |87 and a positivepotential is also applied through the resistancefiagil to the cathodesof thesetriodes, which. .cathodes are vconnectedtogether and througharesistance 2|2 to ground. This arrangement is `such .that While intheabsence oisignals thejanodes ,are positive with respect to the cathodes,the ycathodes are at the same time so far'positivewith respect to thegrids thatthe triodesare normally beyond cut-oli. This cut-off conditioneven exists in thecase ofthe one` of `these triodes whichis connected to`the, conducting triode ofv the pair |32, |34. Brieily, anticipatingamore complete description of operation, the arrangementissuch that,ifthe cathodes are driven more,negative during operation, that triode,the grid of which is connected `to the non-conductingtube 32or |34,neverthelessremains at cut-oli condition; out thetriode which has its`gridconnectedto the conducting tube |32 or |34 becomes conducvelocityyof vthe vehicle which carries the .ap-

paratus may be produced in various fashions of which thatillustrated inFigure -1 is simpler-and wholly satisfactory. .A shaft |93 which rotatesat a speed proportional to the speed of the .vehicle carries a disc. |92provided withrectangular radially arrangedslots which chop the. lightpassing from a lamp |94 to -a photocell |95. The chopping rate hereinvolved is subject to a `Wide range of choice but may be of the order.of 1;,000 to 20,000 cycles, or more, persecond. at l5 miles per hourvelocity of the. vehicle. The vvoltage wave which appears at the grid ofatube |96 is approximately triangular in form. The output from the tubeV|96 is taken off its cathode resistor and fed througna conventionalamplifier |,91to give `amplified pulses in the output line |98 whichfeeds thelast stage tubeilliiofthe amplify-ing system. The anode of thetube|is fed arpositive potentialthrough the resistance, I 88 ..and thenlterl'l which minimizes the transmission of gain or loss. of. pulses mpulses-3110 the anodes of l two atriodesi |19` and im? which are fed apositive potential through the same resistancel.

`The triodes 200` and 2112 areconnected in a conventional fEcclesvJOrdan, triggerl circuit 2 05 bv the criss.cross connection-.softhe grids and anodes orthese ,triodesithrough resistancefcapacity net-Works; ;2|l4 and 20,6. Signals are delivered tothis trigger.circuit;through ,thev Gentlemen-2.93 vturni are deliver@dAf-romtthrouehthe connection' 208 and coudenserm. |20 :to the cathodesffthe triodes i l 82 and 18.4- ;l'heroueration .ofthe :trieser lcircuit isintacsordanceawith ,conventional practice. A negative nulsefdelivered.through the condenser BUS cutsi the-.triade -and rendersconductivethel-triodef292. Vlnegative.pulse is thus produced thrauelt-the.condenser 2 t0. .The condenser 2 L9 and resistance 212- provide adifferentiating circuit with the result that a sharp `narrow negativepulse lisimposeden the'cathodes of the triodes L92 and |84. .Thetriggercircuitis reversed when a positive nulsis transmitted; throushthecondenser 203. However, only the negativepulses produce an eiect atthetriodes |82 and |94 Sine@ only. such.nesatvepulssszwill result. in.driving the cathodes suicientlynegative `to vrc-rnder conductive thattriode the grid kof Whichismore positive than the otherv duetoconduction oli the triode |32 or|,34 tothe cathode-of Ywhich itisconnected. The resultsmay be summarizedby statins that,duringa-l-relativelvlone period of relatively positive grid. potentialone ofthe triodes |,82-.or .|84 Willconduct narrow pulses Vofcur,- rent.corresponding to-each cycle generatedby the ,operationot the disc L92.In any given-period, the .frequency of these pulses will be idilecftlvproportional tothe speed of the vehicle. velocity pulses :should bequitenarrow as de scribed relative tothe: pulses imposed on thegridf, maand lacune, to thefswmgmgor the pendulum. If so, there` isonly yanegligible lossofpulses due to coincidence l-vviththe shift of operationbetweenthetriodes .lzland |84. In atypical systemi t .hasbeen found,foreXample, that the y beeasily kept to less than 25 out of 200,000.

VAt J in ,l'igpre v1.0 there vare indicated the differentiatednegativepulses originating @t the d is c,|.9 2 which drive ythe cathodes oftriodes |82 and. |84 negative. As indicated, their amplitude is greaterthanthe potential diierencesbetween H2 andi- I4 and between I2 and I4.The resulting potential variations. of the anodesofv triodes |84 and, 82arerespectively indicated atK and L in Whichthe plate supplypotentialisindicated by the chain lines.

vThe potentialpulseswl'iich are respectively pro- .fucedet the,- .anQdeS.0f the I triodes |82. .arid "84 .are takenoi through the lines Lf2|8and 220 and condensersf:f2v a n d ;2 24 to; be counted. Condensers |89andj 19| lare. provided to broaden the outputv pulses-tovsimplifyandrender more positive theoperation. of theV counting system. Forconvenience i of f description the pulses r through the line :2|8will-be describedaspositi-ve elevation pulses-and thosethrough theline-220 as negative elevation pulses, it being understood that theseterms refer not to the polarityof the pulses but rather tothe directionsof pendulum deviations which give risetothem. It may be notedthatmaintcnance .of precisely. equal amplitudes of pulses on grids V1.8vand. L89. or ci constant amplitude ofthe cathode pulses is not ofimportance .so lons yas theamplitudes .are Sufficient t0 Cause 11triodes |62Y and |84 to perform their gatingfunctions.

At the frequencies indicated it will beevident that the elevation pulsesfollow each other in too rapid sequence for direct operation ofmechanical counting means. Accordingly, they are scaled down by means ofscaling circuits or counters indicated in Figure 1 at 226 and 22B. Thenature of these scaling Icircuits will bedescribed Vhereafter.Essentially they involve giving rise to single output pulses for groupsof input pulses, for example, in ya ratio such as one output pulse foreach 256 inputpulses. The output pulses from these scaling circuits aredelivered to a differential counter indicated generally at 238. Beforeproceeding with a detailed description` of this diiferential counterthere will be referred to -certain mechanical connections, referencebeing made to Figure 7.

In order to minimize slippage on the roadway (which term is used hereinto refer to any path traversible by thel apparatus, not necessarily awell-defined road,` but including cross-country lines of travel) so asto secure an accurate measurment of the length of path traversed, and inorder to maintain conformity of parallelism of the base of the pendulumapparatus with the road surface there is preferably provided a trailer233. This trailer comprises a rigid frame mounted on three wheelsindicated at 234, 235 and 236. Spring mounting is desirably avoided toeliminate tilting errors to a maximum degree, the tilting due to theresilience of ordinary rubber vehicle tires being,` however, negligible.The wheel 234 1ocated at the mid-portion of one side of the trailer isnormally fixed but is adjustable abouta vertical axis relative to theframe of the trailer through the medium of an adjustable link 255clamped in adjusted positionv by a pair of nuts. The other two Wheelslocated at the front and vrear of the other side of the vehicle frameare dirigible and interconnected. A vertical shaft 231 is connected to atowing bar 238 to be turned thereby and is connected through a parallellinkage indicated at 239 with the front wheel 235. The towing bar 238provides a hitch to a motor driven truck which may carry the electricalportions of the apparatus under observation of an attendant. A verticalshaft 248 is connected througha parallel linkage 24| with the rear wheel238. Pulleys carried bythe Vertical shafts 231 and v240 are connected bycrossed rsteering cables 242 adjustable by means of turn'buckles 245,these steering cables being clamped to the pulleys at 243 and 244. Thearrangement just described is such that as the towing bar 238 isangularly moved about a vertical axis, the vertical plane of the wheel235 remains parallel thereto and the angle of this wheel with respect tothe trailer frame is reproduced but in an opposite sense by the rearwheel 236 by reason of the cable connections. It will, accordingly, beevident that the axes of all three wheels if produced would intersect ata common point. The result is the securing of good tracking of the pathfollowed by the trailer irrespective of banking of the road- Way orother irregularities of the roadway causing it to deviate from a plane.The pendulum assembly is carried by the frame at 24S being arranged tobe leveled by three adjusting screws. This leveling is accomplished whenthe trailer is located upon an accurately horizontal surface preparatoryto the making of a survey. The rear Wheel 236 is provided with a ringgear 248 driving a pinion 249 and through it flexible shafting l2forming a part of the shaft |93 previously de# scribed which drives thedisc |92. The disc |92, the lamp |94, the photocell |95 and the tube,|96 are located within a housing indicated at 241. Gea-red to the shaft|93 is another shaft 252 which drives a recorder chart as hereafterdescribed to produce a displacement of the chart accurately proportionalto the displacement of the trailer along its path. Also geared to theshaft |93 is a small alternating current generator 2511 which will behereafter referred to. This generator produces an alternating current,the frequency of which is proportional to the speed of displacement ofthe trailer along the roadway. The electrical connections from theapparatus on the trailer to that in the truck may be, made throughflexible cables, and the shaft 252 may be in part flexible since therecorder is preferably also in the truck. It may be remarked that all ofthe operating apparatus may bein the truck if desired if there isprovided a Selsyn drive arrangement from the rear wheel 236 to reproducein the truck the displacement of the rear wheel. It will be evident thatthis trailer may take various forms so long as it provides a propermounting for the pendulum assembly, Vthe housing of which must assume atall times the inclination of the roadwayY and so long as a wheel thereofprovides an accurate measurement of the path traversed. A traileraccomplishes this result better than a powerv driven truck because suchtruck is liable to produce substantial errors of inclination and oftracking during changes of speed and under variations of roadwayconditions which involve variable slippage.

Figure 8 illustrates the apparatus inthe differential counter heretoforereferred to as 230. A motor 256 through gearing 251, 258 and 268 drivesa pair of friction discs 262 and 264 which in turn tend to drive ratchetwheels 266 and 268 at speeds in excess of maximum speeds permitted tothem 'by the action of escapements 210 and 212. These escapements areoperated in opposite directions through solenoids. Solenoids 346N and348N control the escapement 210 and solenoids 346iD and 348Peccntrol theescapement 212. These solenoids arerespectively energizedas Will bedescribed hereafter by the negative and positive scaling circuits 228and 226. The shafts 214 and 216 lconnected to the ratchet wheels 266 and2,618 drive a diierential mechanism conventionalized at 218, the formerthrough gearing 280 `and the latter through gearing 282. The outputshaft 234 of this differential mechanism drives a counter 236 whichcounts the sum of the pulses delivered by both scaling circuits.

The shafts 214 and 216 also drive through gearing 290 and 292 a seconddifferential gear mechanism 288, the output shaft 294 of which drives acounter 296 which records the diference of the pulses delivered by thenegative and positive scaling circuits. (It will be noted that there arethree gears at 282 compared with two gears at 280 for producing thecounting of the sum while two gears 290 and two gears 292 provide forthe counting of the difference.) The shaft 252 (Figure 7) drives asindicated in Figure 1 a counter 298 which records, to a suitable scale,the displacement of the vehicle and accordingly the number of pulsesproduced by the slotted disc |92. As will be evident the counts of thecounters 286 and 298, taking into account scaling differences, shouldtheoretically agree, i. e., the sum of the pulses delivered through thelines 2 I8 and 220 should be equal to the pulses produced by thevslotted disc. iActual-ly ftliisiiisnnotv precisely the-case but thereWillibelsomellossin Athefnurnber of pulses throughthe,electri-calrsystemydue to particular coincidence .conditions ias..above mentioned. The `two counters .are provided -in order that a'.check maybemade. o1"` the validity of results since the diierenceinreading. of these counters. will indicatey how many 'pulses havebeenlost and consequently will servezasfa measure `of proper .operation and-of =tl1e .accuracy of l.the

survey.

The reading of the. diierence counterhZQGfand in addition. thedifference of. thecounts indicatedin thecounters 226 and 228, `aswilrbehereater pointed out, 'is the measure of the.v change of elevationuncorrected :for acceleration.

givenA by the displacement` oftheshaft .2943 i. e.,

the counter 296, a`r quantity proportional to V2 the resulting`measurement Will be completely corrested forv acceleration-sothata chartmayi'becaused-to record continuously-while-the vehicle is moving,theelevational vdi-ierence Iwhich Mis encountered. This correction'isexact fori-restored pendulum systems ofthe typedescribedherein and isapproximatefor displaced pendulums for small angles -of inclination. Ofcourse,iif the vehicle is brought to-rest this'correction disappears andthe difference in l elevation between two rest positions mayy be readdirectly from the counter 2x96:and-indicating-bulbs in the-scalingcircuits. A major ladvantage in using a 4restored pendulum system -incontrast there is utilized the generator-254 previouslyl de-` scribed inconnection with Figure? and shown in itselectrical connections-inFigure 1. The generator 25d is a conventional alternating `cur.- rentgenerator having ypermanent magnet. poles. The output voltage isaccordingly directly'proportional to the speed of thevehicle sinceit'isdriven from the rear Wheelandrthe-speed-may be read from an A.C.voltmeter l3nt -in .ser-ies with a resistance 303- suiciently high toprevent substantial currenty drain on-the-` generator 22154. Thefrequency of its outputiis also'directly'proportional to t'ne speed ofthe'vehicle. "Fliegenerator feedsy a series arrangementof-a high`resistance `3534 and an inductance 1392. `Since the impedance of Y theinductance A'SI12-varies directly v as the frequency it will be evidentthat the alternating potential across this inductance willbe directlyproportional to the square offtheivelocity involved in the correction. Aldiode 306 and potentiometer resistance '-308 together'v-With arcapacity 309 are connected across-the inductance 3021to provide a directpotential on'the grid of the tube 3m, which potentiall-is-substantial-ly proportional to the squareof the velocity. The

factor of proportionality may yloe-adjusted by changing the position offthe vpotention'leter contact. A second tube'3l6 is arranged in parallelWith the tubefSiil and the twotubes are provided with equalcathoderesistors .3!3 and l3H?.

1 The shaft 294 of the differential counter (Figure 8) is connected(through reduction gearing, not indicated) to --operateithe movablecontact 3 I2 -of a potentiometer 3 l4\-energized Lvbyffa vwhat It can beshown that by adding algebraically tothe value teryso-:astovarythepotential ofthegrid ofthe tube 131.6; The `diierence of potentials.between the; two.A eathodes taken off through'. .the lines4 3 I 'Iand3l8 serves to operate a. conventional recorder 30.0, for example, ofthe EasterlinefAngus type, the chart of which is. driven .'fromthe.shaft252 so-that agraphUWi-llbe drawn, the abscissae of W-lnolnisproportional to the road; distance transversed andithefordinates ofwhichwill-be proportionaltto ther-difference i in .f elevation continuouslycorrected :for velocity.

.Figure 9, illustrates the vtype of `scaling-circuit which; may be usedat b'othJZZB and .228. Since these may be identical Figure 9-.Willserveto illustrataboth. The lineffrom condenserf222 orfrom condenser 224 isconnected toan attenuator 320 through which .the pulses aredelivered. to:the conventional amplifying stages :322 andzf3`24, the amplinedpulses:being delivered-through. the'. line v3 28and condenser ;':328. KThecounter.comprises aseries-'of identical stagesionly. onelof twhichi isillustrated at 132B, it being.A understood-thatfthis isi-followed by aseries of similar. stages completed by-the: last stage 33A tor whichoutput. connections are made. ther-pulses in a-ratio of 2:1. lItfhasbeenwfoun'd convenient, With the. frequencies describedv above,toprovide. eight of these stagesto giveascaling ratio of 256:1. Theelements. of each scaling i stage'are quite conventionalandrequirenoparticular specialdescription. v'Each .comprises a doubletriode336 with aneon; or similarlampa332 provided in thestage.toindicaterthecount represented thereby. Thedouble triodefof:thelast Stage 3 34 is. indicatedat1,313.61and1the ,neon ytube thereinis illustrated at 338.

These counters with :somewhat `morei complicated interconnections may bemade. to scalein the decimal system Arather than-iinthezbina-ry systembut for present .purposesthe binarynsystemv is; quite .-suiiicient whendue account, is taken ofl the Yfact that; theA residual countrepresentedv by the illuminated neon tubes, must, be read inaccordancetherewith. At any. instant the number of 'pulses may beaccurately determined, by readingzthe. counter -2-96 y in terms of.multiples4 of :5256 and -f adding' to :that -reading the diierence :indigits represented bytheneon lamps lit vin .the two scali-ngcircuits.

.The output fromthe last stage-of. each-scaling circuit .is-takenmhroughlinesitlm vand, 342 tota push-pull amplier arrangement.Slidiwhichzserves Yfor selective energizing of the solenoids 3345 and348, previously described, which operate the escapements.

' The ffact that the apparatus, described lymeas-v bythe integralbetween initial and terminal.

points cfg-instantaneous velocity multipliedby the instantaneous sine of.thefangle of. inclination of the path withrespect totime. 'A closeapproximation .to thisintegral cantbe easilyshowneto result if instead.of the. instantaneousvalue ofthe sine ofthe angleof inclinationvthereis.taken over small inter-val increments the statistical value ofthe sine of the-.angle of inclinationsuch as might 3be Adetermined byconsidering .the average angle of inclination of r.a .swinging pendulumwith respect ,to a roadway and gf,: .l'z11 stead of an exact; measure ofinstantaneous velocity, -thereis substitutedthe number of ,integralpulses per unit time statistically proportionalto;

the velocity.

Each of these lstages scales down` `The tangential force or torquenecessary to maintain a pendulum precisely perpendicular to a roadwaywhich has aparticularangle of slope is proportional to the sine of theangle of slope. Furthermore, if a pendulum is constrained to oscillateabout such a position perpendicular to a roadway by the application ofequal and opposite forces of constant magnitude applied throughirregular intervals the net force, proportional to the differences intimes of application of the two equal and opposite forces, will beproportional to the sine of the angle of inclination. The sine of theangle of inclination may accordingly be measured by measuring suchdifferences in time of the application of the equal and opposite forces.

. In curve G of Figure 10 the times of flow of pendulum current in onedirection less the times of flow of equal current in the oppositedirection would be such a measure of the sine of the angle ofinclination. One type of statistical evaluation of the required integralcould involve the Ineasurement of these relative times over an extendedtime or space interval with multiplication then by a quantityproportional to the average velocity through that interval. It will beevident, however, that the same statistical result would be accomplishedif there is counted during any interval of flow of pendulum current inone direction the number of pulses having a frequency proportional tovelocity which are produced during that interval and algebraicallysumming such counts, calling them positive when pendulum current isflowing in one direction and negative when it is flowing in the otherdirection. It is in this last fashion that the statistical integrationis accomplished in the present apparatus. Curves K and L of Figure 10respectively show the number of pulses which are counted by theapparatus during pendulum current flow in one direction and the other.The difference of these counts is observed or recorded. It will beevident, and can be readily shown, that the statistical approximationbecomes better and better as the frequency of reversal of the currentthrough the pendulum is increased and as the number of pulsescorresponding to a given velocity is increased. Under conditions such asstated heretofore the statistical measurement attains a high degree ofaccuracy with, for practical purposes, errors which are quitenegligible. Errors do, of course, theoretically exist. The pendulumcurrents flowing in the two directions must be made equal to aconsiderable degree of accuracy. Changes of frequency of pulsesproportional to velocity occurring during pulses of pendulum currentflow will theoretically affect the accuracy, but actually withfrequencies of pendulum oscillation such as stated the errors due tothis cause are of a very low order of magnitude. Another error may arisein the system due to the loss of counts by coincidences of velocitypulses with change-overs in the direction of current flow. However, itis found in practice that these losses of counts are negligible if thevelocity pulses applied to the cathodes of triodes |80 and IBI are keptvery narrow in comparison with the width of the pulses of pendulumcurrent. Furthermore, the apparatus provides a continuous check on thistype of error by permitting the comparison of the reading of counter 298with the reading of counter 236. The extent to which the readings ofthese counters correspond is a direct measure of the loss of counts.

It may be noted that a loss (or gain) of pulses does'not contributedirectly to an uncompensated error in the difference since the circuitcan be so adjusted that the loss or gain is approximately equal forpositive and negative pulses. So long as the fraction of pulses lost bythe positive and negative counters remain constant, the error variesfrom no error at all to a fixed error which can be compensated by adrift correction.

While the invention has been described in connection with a type ofapparatusin which it achieves special utility it may be pointed out thatthe invention is of very much broader scope. There is fundamentallyinvolved the integration of the product of two functions with respect toan independent variable which, as will be evident in theforegoing, ismeasured in terms of time but may well'be fundamentally anotherindependent variable whichfby transformation of the integral in thepresent case happens to be displacement. The principles of the inventionare thus quite broadly applicable to the integration of the product(and, of course, by considering one function as the reciprocal ofanother function, of the quotient) of two functions. It is onlynecessary that one function be represented by a difference of timeintervals (as represented by curve G of Figure l0) and that the otherfunction be represented by pulses (as in curve J of Figure 10) with theprovision of the equivalent of the system described to count thedifference of the pulses occurring during respective intervals assignedpositive and negative designations. As will be pointed out in discussionof further modifications, these results may be achieved in numerousways, including those involving known equivalents of the variouselements cf the apparatus already described.

Aside from the matter of integration just discussed there may also bepointed out another aspect of invention involved in what has beendescribed, namely, the measurement statistically of a force (or of aposition or other quantity dependent on the force or'on which the forcemay be said to be dependent) by producing in a statistical sense anaverage null position of a member displaceable by the force. rI'hependulum which has been described may be considered in this respectmerely an example of a member subject to displacement by a force, in thepresent instance gravity. Such a displaceable element may be held to amean position by the application of opposite forces applied`periodically during unequal time intervals. As in the describedapparatus these forces may impose on the member an unnatural period ofoscillation about the mean position. The algebraic sum of the intervalsof application of the opposed forces, exemplified by the curve G inFigure l0, will be a measure of the original displacing force or othervariable quantity related to that force. If, for example, in thedescribed apparatus the disc |92 were driven at a constant speed thenumber of counts in some unit interval would then always be proportionalto such force or other related variable. The angle of inclination of apendulum with respect to some datum line could thus by the presentapparatus be remotely teiemetered for any desired purposes.

Before proceeding with discussions of rather different embodiments ofthe invention reference may be made to modifications of the describedapparatus typical of those which will readily occur to those skilled inthe art. It will, of course, be evident that the supply of alternatingcurrent to the pendulum, described as accomplished by the oscillator 30,may be from any other equiv- 17 alent generators, including otheroscillators, light chopping devices, electromagnetic generatorsor thelike. The detectingmeansfr'givi'ng'rise to a control potential uponthedisplacem ht of a pendulum or other force-displaceablefdevice maytake numerous forms 'of which the'pliase detector illustrated is merelyan example, though, nevertheless, one to be preferred i'iiyiewf itsindependence of amplitude of fthe'signal'with'l'redulum may be actedupon bya series' of pulsesl in one direction and then a seriesof'fpulss` in the opposite direction with lconsecuen similar operationsin other parts of the circuit. While yfor simplicity the opposingAelectrmechariical JOY.

forces may be best applied to the'pei'i'dul' reversal of current'through the entire" cell Y Will be evident that this coil may besplit sthat current in one direction flows through"one` of its halves andcurrentin the other direction hows through another of its halves. Or"further,"sev veral separate coils may be wound on the pendulum,separating completely the rents and/or the detectingandrestoring-currents. It will also be evident that the functions of thependulum and neld coils maybeinterchanged. Further, a gyroscope may vbesubstrtuted for the pendulum. The lfunctie nlrepresented by velocity inthe described apparatus Y:may be transformed into equivalentlpulses`,in`- v ery many other Ways than that illustrated# -The `lightchopping arrangement may be QDlf-d by a generator having -a frequencyoutput dependent on speed, with suitable Wave shaping devices of knowntype for the purpose of securing narrow pulses controllable by thelonger pulses due to a second variable. The counting means-is alsolsusceptible to numerous changes among which may be cited reversible,motors or motors' of variable speed connected to diierential mechanismscapable of giving not integral numbers of counts but rather continuousoutput displace* ments representing to a sufhcient degreecf accuracy thenumber oit differential countsasherein described. rlhe velocitycorrection may `also be provided in numerous ways of whicha-,centiiiugalgovernor arrangement may be con deredv most obvious. k

It may be noted that in asystem of the general type described, as wellas in systems hereafter described, particularly when extreme accuracy isnot required, simplification, involvingelimina:

tion of one scaling circuit, maybe effected by counting pulses of onlyone type (positive or negative) and the sum of the pulses correspondingto those produced by disc i972, this'latter count being accomplished,for example, bya Vcounter such as 293. Under such yconditions thedifference P-N of positive and lnegativelpulses is secured as the sumP-i-N minus 2P' or l Figure 11 indicates a modication ofthe invention inwhich feed back to the pendulum i's` provided in a different'fashionthan thatwh'eretofore described and in"whiclfrth'e` recording is "alsodifferently accomplished. 'I o si h iplify the disclosure there areillustrated in comparison withligure 1 only lthose elements which difierfrmequivalent"counterparts in Figure 1."[In various instances referencenumerals are used corresponding to those'in Figure 1 with the addi-`tion'of'prime's.' """lhesystem'of Figure 11 is similar to that ofFigure "'1from thek pendulum'through -the amfyin'gand phase.` detectingmeanswith there- 1o ,1t 'thatrdir'ect potentials are. produced in the""nhes" and-98." corresponding toet and 98refs'p'ectively; thesepotentialsv having signs depend- 'fi upon-thedirectionofdeviation ofthepen- 'dulum from" a' position normal tothe roadway. 1 5 The lines 86'and 9&3 feed a direct'current amienil which serves to drive in reversingfashion `control motor 352'. The direct current "iampliiierfmay be ofany'of various' conventional suitable forv driving a motor 352' tosecure 20"'. rsumcieiit"ri'iechanicai power output for purhreafterdescrilzaed.' It may, for example,

wrllevelto drive a :rnotcrr capable of quick'rersalin accordance 'withthe sign of the signal dwith `su`cient power to drive themechani-"cal"'element's`of the apparatus. The particular characteristics of themotor, such as variable or constant" speed' characteristics' or thelike, are

unimportant. i f

`1The' 'shafting 354 of the motor which is confventionali'zed, since itmay include reduction gearing or 'other mechanical transmission ele-40"`rnent`s", drives? the movable contact 356 of apoj tentiometerenergized as indicated by bat- 'teries 1363 and V362vto kprovidefeed-back current f 'ft the "pendulum` coil through the lines i60 and"'l .62"corresponding respectively to I 6i! 'and ll62 ,ofligureli Brieystated, the motor 352 will "",folloiif'in direction of movement thedeviations vofthe'pend'ulux'n from null position and by control of'thep'otentiometer will cause a restoring "fcurrenttolowin the pendulumcoil. Hunting 'of,`th'e system" may be reduced in any-convenf""ti onal`fashion, for example, byv a feed-back throughthe'condenser 35i to theamplier 350. Irrespectiveof thewa've form of the pendulum restoringcurrent (which will'have a direct'jcom- 5 5mpovn'ent`vand 'a'sinuous'alternating component), v[the average current through' the pendulum'coil "Wilbe"'proportional'to the sine of the angle of inclination o 'f'theroadway; and the averagepoiti'onof the 'shaft'l will lalsocorrespondu 1inry thereto","if, as is desirable to avoid thenesityfonmaking" corrections, the potentiometer 'des an output-potentiallinearly related to mjeritbeing 'theamplication to a suflici'ent"ac-incas sleeve 380 providing one input to a differential geararrangement 382. Bevel gears 384 and sleeve 386 provide a second inputto the differential gear arrangement from the shaft 318. The outputshaft 294 of the differential gear arrangement corresponds to the shaft29A of Figure 1 and from that point on the apparatus is again the samevas in Figure 1, including the velocity correction system and therecorder 306, the chart of which is driven from the shaft 252'.

The disc 366 of the integrator is driven from the shaft 252' at a speedproportional to the velocity of the vehicle. For zero inclination angleof the pendulum the ball followers 314 are adjusted at a disc radius todrive the drum 316 at the same speed as the input at 380 to thedifferential. Hence there is no rotation at this time of the shaft 294.This dierential arrangement is used to eliminate operation at or closeto the center of the disc 314 which constitutes yan inaccurate portionof the operating range of the integrator. The position of the balls 314is proportional to the sine of the angle of inclination of the roadwayand hence the rotation of the shaft 294 is proportional to the integralof the sine of the angle of inclination of the roadway with respect todisplacement. The displacement of the shaft 294 may be calibrated inelevation uncorrected for velocity, which correction is achieved as inFigure 1 for continuous recordlng.

As an illustration of the fashion in which pulse counting may be used toprovide the value of an integral other than as disclosed in Figure 1,reference may be made to Figure 12 which shows a modification of aportion of Figure 1. The system now under discussion contains the sameelements as Figure 1 from the pendulum coil, illustrated in Figure 12 at2', through the condensers 43* corresponding to condensers 43 and thesubsequent amplifying and phase detecting devices, including thethyratrons los and |65, through the condensers |24' and |26corresponding to |24 and |26. Certain changes illustrated in Figure 1 2are then involved up to the lines |16' and |12 corresponding to |10 and|12 and the lines |60 and 162' corresponding to lines |66 and |62 whichprovide feed-back current to the pendulum coil.

In the modiiication of Figure 1 the signals applied to the control'.grids, of the thyratrons |04 and |06 were such that one or the other ofthese thyratrons'would be cut off while the other was pulsing. Foroperation in accordance with the present system the thyratron biases aresuitably adjusted and the amplifier gain is so reduced that thethyratrons are not cut oif but rather both of them pulse continuously.Adjustment is initially made so that the two thyratrons pulse at equalrates when the pendulum is in null position. When the pendulum deviatesfrom this position a more negative potential is applied to thecorresponding one of the thyratrons and its pulse rate is decreased.This variation in pulse rate is caused to control the feed-back and thelrecording through the elements illustrated in Figure 12.

A pair of triodes 388 and 390 are connected to form a conventionalrectangular pulse generator by criss-cross connections of their gridsand anodes, including a condenser 396 and a resistor 398. Thisarrangement is connected to receive 20 the sharp pulses from thecondenser |211'.V A similar circuit comprising the triodes 392 and 394and connections including the condenser 40B and resistor 462 isconnected to the condenser The rectangular pulse generators are of aparticular type which may be described by reference to the upper one. Anarrow negative pulse delivered through the condenser |24 will cut offthe triode 388 and render conductive the triode 390. Then this conditioncontinues for aV time depending upon the values of condenser 396 andresistance 398. At the end of this time a sharp reversal of conditionsoccurs, the triode 390 being cut oif and the triode 388 being againrendered conductive, this last condition being maintained until anothernegative pulse is applied to the grid of triode 386 through thecondenser |24. The result is that positive rectangular pulses aredelivered through connection 464 from the grid of triode 396 at afrequency corresponding to the frequency of negative pulses through thecondenser |24 but of a constant width irrespective of this frequency.The average positive potential of the grid of tube 1168 is thusdependent upon the frequency. Adjustments are originally so made that,considering the frequency of pulses through the condenser |24 when thependulum is in null position the length of the rectangular pulsescorresponding to conductivity of the triode 39u is such that this tubeis conducting almost all of the time. All of the considerations justdiscussed apply equally to the lower rectangular generator.

The grid of the triode 39|) is connected at Mid to the grid of thetriode 153. Similarly, the grid of the triode 394 is connected to thegrid of a triode dit. rlfhe anodes of the triodes i613 and M6 areconnected through resistances [552 and 414 to a battery M5. A low passlter H6 is connected to the anodes and serves to pass smoothed out,though varying, current to the pendulum coil 2 through connections itand i132. In this case if the lter passes only extremely low frequenciesthe result is to apply to the pendulum what amounts to a slowly varyingcurrent maintaining he pendulum substantially steady in the vicinity ofnull position. In fact, even though pulses are fed to the pendulum, asubstantially non-oscillating positioning of the pendulum may besecured, i. e., the pendulum would not pass through null. In eiect itmay be maintained substantially at null by repeated light blows. Thisresult could be accomplished by a simple modification of Figure 12involving causing a constant current 'to flow from a battery through thependulum coil, this constant current being opposed by pulses in onedirection only.

As in the case of the modification of Figure 1 the average feed-backcurrent to the pendulum depends on the difference of the average valuesof what may be called positive and negative rectangular pulses. However,in contrast with Figure 1 n1 which these pulses were successive thepulses in the present modification are not successive but may overlap ina rather random fashion, as may be dictated by their differentfrequencies by their constant duration. Their algebraic difference isthe current fed to the pendulum coil. These pulses are fed through theconnections |16 and |12', corresponding to i193 and |12 in Figure 1, toa similar integrating system in which they are used for gating sharppulses originating from the velocity input. Again the negative

